<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            margin: 0;
        }
        nav {
            width: 100vw;
            height: 80px;
            border-top: 1px solid black;
            position: fixed;
            bottom: 0;
            font-size: 0;
        }
        nav>div {
            width: 25%;
            height: 100%;
            border-right: 1px solid black;
            /* 改变盒子模型 */
            box-sizing: border-box;
            /* float: left; */
            display: inline-block;
            background-color: red;
        }
        nav>div:last-child {
            border: none;
        }
    </style>
</head>
<body>
    <nav>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
    </nav>
</body>
</html>